As is well known, as represented by a glass substrate for a flat panel display (FPD) such as a liquid crystal display, a plasma display, or an organic light-emitting diode (OLED) display, glass sheets utilized in various fields are actually required to satisfy a rigorous product quality requirement for surface defects and waviness.
Therefore, in order to satisfy such a requirement, an overflow downdraw method is widely employed as a method of manufacturing a glass sheet.
As illustrated in FIG. 11, this manufacturing method includes: pouring molten glass Gm into an overflow trough 2 formed in a top portion of a forming device 1; causing the molten glass Gm, which has overflowed to both sides from the overflow trough 2, to flow downward along outer surface portions 3 (each including a perpendicular surface portion 3a and an inclined surface portion 3b) of the forming device 1 having a substantially wedge shape; and fusing streams of the molten glass G together at a lower edge 4 of the forming device 1, thereby continuously forming a single glass sheet G. This manufacturing method has a feature in that both front and back surfaces of the glass sheet G thus formed are formed in a forming process without coming into contact with any area of the forming device 1, and hence a fire polished surface with extremely high flatness and smoothness and without defects such as flaws can be obtained.
Note that, the forming device 1 includes a guide wall portions 5 on both widthwise end portions (see, for example, JP 2008-526671 A and JP 2008-539159 A). Both widthwise end portions of the molten glass Gm, which has overflowed from the overflow trough 2, are guided downward along end surfaces of the guide wall portions 5 at a stage at which the molten glass G has reached the outer surface portions 3 of the forming device 1.
Further, for the purpose of suppressing contraction of the glass sheet G in the width direction, at a position immediately below the forming device 1, both widthwise edge portions of the glass sheet G are nipped by pairs of edge rollers (cooling rollers) 6 from both the front and back sides of the glass sheet G.